Showing papers on "Energy (signal processing) published in 2018"

Improved Limit on Neutrinoless Double-$\beta$ Decay of $^{76}$Ge from GERDA Phase II

Abstract: The GERDA experiment searches for the lepton-number-violating neutrinoless double-β decay of ^{76}Ge (^{76}Ge→^{76}Se+2e^{-}) operating bare Ge diodes with an enriched ^{76}Ge fraction in liquid argon. The exposure for broad-energy germanium type (BEGe) detectors is increased threefold with respect to our previous data release. The BEGe detectors feature an excellent background suppression from the analysis of the time profile of the detector signals. In the analysis window a background level of 1.0_{-0.4}^{+0.6}×10^{-3} counts/(keV kg yr) has been achieved; if normalized to the energy resolution this is the lowest ever achieved in any 0νββ experiment. No signal is observed and a new 90% C.L. lower limit for the half-life of 8.0×10^{25} yr is placed when combining with our previous data. The expected median sensitivity assuming no signal is 5.8×10^{25} yr.

GW170817: Constraining the nuclear matter equation of state from the neutron star tidal deformability

Abstract: Constraints set on key parameters of the nuclear matter equation of state (EoS) by the values of the tidal deformability, inferred from GW170817, are examined by using a diverse set of relativistic and nonrelativistic mean-field models. These models are consistent with bulk properties of finite nuclei as well as with the observed lower bound on the maximum mass of neutron star $\ensuremath{\approx}2{M}_{\ensuremath{\bigodot}}$. The tidal deformability shows a strong correlation with specific linear combinations of the isoscalar and isovector nuclear matter parameters associated with the EoS. Such correlations suggest that a precise value of the tidal deformability can put tight bounds on several EoS parameters, in particular on the slope of the incompressibility and the curvature of the symmetry energy. The tidal deformability obtained from the GW170817 and its UV, optical and infrared counterpart sets the radius of a canonical $1.4{M}_{\ensuremath{\bigodot}}$ neutron star to be $11.82\ensuremath{\le}{R}_{1.4}\ensuremath{\le}13.72\phantom{\rule{4pt}{0ex}}\mathrm{km}$.

Measurement of the Electron Antineutrino Oscillation with 1958 Days of Operation at Daya Bay

Abstract: We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor ν[over ¯]_{e} inverse β decay candidates observed over 1958 days of data collection. The installation of a flash analog-to-digital converter readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration to less than 0.5% for visible energies larger than 2 MeV. The uncertainty in the cosmogenic ^{9}Li and ^{8}He background is reduced from 45% to 30% in the near detectors. A detailed investigation of the spent nuclear fuel history improves its uncertainty from 100% to 30%. Analysis of the relative ν[over ¯]_{e} rates and energy spectra among detectors yields sin^{2}2θ_{13}=0.0856±0.0029 and Δm_{32}^{2}=(2.471_{-0.070}^{+0.068})×10^{-3} eV^{2} assuming the normal hierarchy, and Δm_{32}^{2}=-(2.575_{-0.070}^{+0.068})×10^{-3} eV^{2} assuming the inverted hierarchy.

RF-based Energy Harvesting in Decode-and-Forward Relaying Systems: Ergodic and Outage Capacities

Abstract: Radio-frequency energy harvesting constitutes an effective way to prolong the lifetime of wireless networks, wean communication devices off the battery and power line, benefit the energy saving and lower the carbon footprint of wireless communications. In this paper, an interference aided energy harvesting scheme is proposed for cooperative relaying systems, where energy-constrained relays harvest energy from the received information signal and co-channel interference signals, and then use that harvested energy to forward the correctly decoded signal to the destination. The time-switching scheme (TS), in which the receiver switches between decoding information and harvesting energy, as well as the power-splitting scheme (PS), where a portion of the received power is used for energy harvesting and the remaining power is utilized for information processing, are adopted separately. Applying the proposed energy harvesting approach to a decode-and-forward relaying system with the three-terminal model, the analytical expressions of the ergodic capacity and the outage capacity are derived, and the corresponding achievable throughputs are determined. Comparative results are provided and show that PS is superior to TS at high signal-to-noise ratio (SNR) in terms of throughput, while at low SNR, TS outperforms PS. Furthermore, considering different interference power distributions with equal aggregate interference power at the relay, the corresponding system capacity relationship, i.e., the ordering of capacities, is obtained.

Energy-Efficient Admission of Delay-Sensitive Tasks for Mobile Edge Computing

Abstract: Task admission is critical to delay-sensitive applications in mobile edge computing, but is technically challenging due to its combinatorial mixed nature and consequently limited scalability. We propose an asymptotically optimal task admission approach which is able to guarantee task delays and achieve $(1-\epsilon)$ -approximation of the computationally prohibitive maximum energy saving at a time-complexity linearly scaling with devices. $\epsilon $ is linear to the quantization interval of energy. The key idea is to transform the mixed integer programming of task admission to an integer programming (IP) problem with the optimal substructure by pre-admitting resource-restrained devices. Another important aspect is a new quantized dynamic programming algorithm which we develop to exploit the optimal substructure and solve the IP. The quantization interval of energy is optimized to achieve an $[\mathcal {O}(\epsilon),\mathcal {O}(1/\epsilon)]$ -tradeoff between the optimality loss and time complexity of the algorithm. Simulations show that our approach is able to dramatically enhance the scalability of task admission at a marginal cost of extra energy, as compared with the optimal branch and bound method, and can be efficiently implemented for online programming.

Advances in solar photovoltaic tracking systems: A review

Abstract: Solar photovoltaic technology is one of the most important resources of renewable energy. However, the current solar photovoltaic systems have significant drawbacks, such as high costs compared to fossil fuel energy resources, low efficiency, and intermittency. Capturing maximum energy from the sun by using photovoltaic systems is challenging. Several factors that affect the energy output of such systems include the photovoltaic material, geographical location of solar irradiances, ambient temperature and weather, angle of sun incidence, and orientation of the panel. This study reviews the principles and mechanisms of photovoltaic tracking systems to determine the best panel orientation. The tracking techniques, efficiency, performance, advantages, and disadvantages of simple tracking systems are compared with those of state-of-the-art tracking systems. Diverse types of solar tracking systems based on their technologies and driving methods will be presented and categorized.The future trends of tracking systems are also highlighted.

Measurement of Reactor Antineutrino Oscillation Amplitude and Frequency at RENO.

Abstract: The RENO experiment reports more precisely measured values of θ_{13} and |Δm_{ee}^{2}| using ∼2200 live days of data. The amplitude and frequency of reactor electron antineutrino (ν[over ¯]_{e}) oscillation are measured by comparing the prompt signal spectra obtained from two identical near and far detectors. In the period between August 2011 and February 2018, the far (near) detector observed 103 212 (850 666) ν[over ¯]_{e} candidate events with a background fraction of 4.8% (2.0%). A clear energy and baseline dependent disappearance of reactor ν[over ¯]_{e} is observed in the deficit of the measured number of ν[over ¯]_{e}. Based on the measured far-to-near ratio of prompt spectra, we obtain sin^{2}2θ_{13}=0.0896±0.0048(stat)±0.0047(syst) and |Δm_{ee}^{2}|=[2.68±0.12(stat)±0.07(syst)]×10^{-3} eV^{2}.

Implementing nonlinear Compton scattering beyond the local constant field approximation

Abstract: In the calculation of probabilities of physical processes occurring in a background classical field, the local-constant-field approximation (LCFA) relies on the possibility of neglecting the space-time variation of the external field within the region of formation of the process. This approximation is widely employed in strong-field QED as it allows one to evaluate probabilities of processes occurring in arbitrary electromagnetic fields starting from the corresponding quantities computed in a constant electromagnetic field. Here, we scrutinize the validity of the LCFA in the case of nonlinear Compton scattering focusing on the role played by the energy of the emitted photon on the formation length of this process. In particular, we derive analytically the asymptotic behavior of the emission probability per unit of photon light-cone energy ${k}_{\ensuremath{-}}$ and show that it tends to a constant for ${k}_{\ensuremath{-}}\ensuremath{\rightarrow}0$. With numerical codes being an essential tool for the interpretation of present and upcoming experiments in strong-field QED, we obtained an improved approximation for the photon emission probability, implemented it numerically, and showed that it amends the inaccurate behavior of the LCFA in the infrared region, such that it is in qualitative and good quantitative agreement with the full strong-field QED probability also in the infrared region.

Galactic rotation curves versus ultralight dark matter: Implications of the soliton-host halo relation

Abstract: Bosonic ultralight dark matter (ULDM) would form cored density distributions at the center of galaxies. These cores, seen in numerical simulations, admit analytic description as the lowest energy bound state solution (``soliton'') of the Schroedinger-Poisson equations. Numerical simulations of ULDM galactic halos find empirical scaling relations between the mass of the large-scale host halo and the mass of the central soliton. We discuss how the simulation results of different groups can be understood in terms of the basic properties of the soliton. Importantly, simulations imply that the energy per unit mass in the soliton and in the virialized host halo should be approximately equal. This relation lends itself to observational tests because it predicts that the peak circular velocity, measured for the host halo in the outskirts of the galaxy, should approximately repeat itself in the central region. Contrasting this prediction with the measured rotation curves of well-resolved nearby galaxies, we show that ULDM in the mass range $m\ensuremath{\sim}({10}^{\ensuremath{-}22}\textdiv{}{10}^{\ensuremath{-}21})\text{ }\text{ }\mathrm{eV}$, which has been invoked as a possible solution to the small-scale puzzles of $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, is in tension with the data. We suggest that a dedicated analysis of the Milky Way inner gravitational potential could probe ULDM up to $m\ensuremath{\lesssim}{10}^{\ensuremath{-}19}\text{ }\text{ }\mathrm{eV}$.

Electrical Switching of Antiferromagnetic Mn 2 Au and the Role of Thermal Activation

Abstract: Current-induced switching via N\'eel spin-orbit torque in thin films of the antiferromagnet Mn${}_{2}$Au offers the prospect of a magnetic multilevel nonvolatile memory cell. The authors investigate this switching with experiments and modeling, explaining the strong dependence of the switching amplitude on current density and temperature. They also point out the importance of thermal assistance of the electrical current to the switching. The energy barrier to switching in Mn${}_{2}$Au is high enough to preserve a magnetic state for many years at room temperature, making this system suitable for real-world spintronic devices.

Equalization of Lithium-Ion Battery Pack Based on Fuzzy Logic Control in Electric Vehicle

Abstract: A nondissipative equalization scheme based on fuzzy logic control (FLC) is presented to improve the inconsistency of series-connected Lithium-ion batteries. The two-stage bidirectional equalization circuit with energy transferring inductors is designed to implement the equalization of cell to cell for battery packs, and the equalization circuit paves the way for module-based equalization of hardware. Equalization based on the state of charge (SOC) is proposed in this paper, and the Thevenin equivalent circuit model of the Lithium-ion battery, as well as the extended Kalman filter (EKF) algorithm, is employed for SOC estimation. For effective equalization, the FLC is proposed to reduce energy consumption and equalization time. The FLC strategy is constructed with a set of membership functions to describe the equalization behavior of the cell. A comparison of the proposed FLC with the mean-difference algorithm is carried out to validate the advantages of the proposed scheme. Simulation results show that the standard deviation of final SOC reduces by ${\text{18}}{\text{.5}}\%$ , and equalization time decreases by ${\text{23}}\%$ for FLC compared with the mean-difference algorithm under new European driving cycle working conditions. The energy efficiency improves by ${\text{5}}{\text{.54}}\%$ compared with the mean-difference algorithm. In addition, the two-stage bidirectional equalization circuit has good performance and improves the inconsistency.

21 cm limits on decaying dark matter and primordial black holes

Abstract: Recently the Experiment to Detect the Global Epoch of Reionization Signature reported the detection of a 21 cm absorption signal stronger than astrophysical expectations. In this paper we study the impact of radiation from dark matter (DM) decay and primordial black holes (PBHs) on the 21 cm radiation temperature in the reionization epoch, and impose a constraint on the decaying dark matter and PBH energy injection in the intergalactic medium, which can heat up neutral hydrogen gas and weaken the 21 cm absorption signal. We assume a strong coupling limit in the Lyman-$\ensuremath{\alpha}$ background and consider decay channels $\mathrm{DM}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}},\ensuremath{\gamma}\ensuremath{\gamma}$, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$, $b\overline{b}$ and the $1{0}^{15--17}\text{ }\text{ }\mathrm{g}$ mass range for primordial black holes, and require that the heating of the neutral hydrogen does not negate the 21 cm absorption signal. For ${e}^{+}{e}^{\ensuremath{-}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$ final states and PBH cases we find strong 21 cm bounds that can be more stringent than the current extragalactic diffuse photon bounds. For the $\mathrm{DM}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ channel, the lifetime bound is ${\ensuremath{\tau}}_{\mathrm{DM}}g{10}^{27}\text{ }\text{ }\mathrm{s}$ for sub-GeV dark matter. The bound is ${\ensuremath{\tau}}_{\mathrm{DM}}\ensuremath{\ge}{10}^{26}\text{ }\text{ }\mathrm{s}$ for the sub-GeV $\mathrm{DM}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ channel and reaches $1{0}^{27}\text{ }\text{ }\mathrm{s}$ for MeV DM. For $b\overline{b}$ and ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ cases, the 21 cm constraint is better than all the existing constraints for ${m}_{\mathrm{DM}}l30\text{ }\text{ }\mathrm{GeV}$ where the bound on ${\ensuremath{\tau}}_{\mathrm{DM}}\ensuremath{\ge}{10}^{26}\text{ }\text{ }\mathrm{s}$. For both DM decay and primordial black hole cases, the 21 cm bounds significantly improve over the cosmic microwave background damping limits from Planck data.

Search for high-mass resonances in dilepton final states in proton-proton collisions at √s = 13 TeV

Abstract: A search is presented for new high-mass resonances decaying into electron or muon pairs. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 36 fb$^{−1}$. Observations are in agreement with standard model expectations. Upper limits on the product of a new resonance production cross section and branching fraction to dileptons are calculated in a model-independent manner. This permits the interpretation of the limits in models predicting a narrow dielectron or dimuon resonance. A scan of different intrinsic width hypotheses is performed. Limits are set on the masses of various hypothetical particles. For the $ {Z}_{\mathrm{SSM}}^{\prime}\left({Z}_{{}^{\psi}}^{\prime}\right) $ particle, which arises in the sequential standard model (superstring-inspired model), a lower mass limit of 4.50 (3.90) TeV is set at 95% confidence level. The lightest Kaluza-Klein graviton arising in the Randall-Sundrum model of extra dimensions, with coupling parameters k/M$_{Pl}$ of 0.01, 0.05, and 0.10, is excluded at 95% confidence level below 2.10, 3.65, and 4.25 TeV, respectively. In a simplified model of dark matter production via a vector or axial vector mediator, limits at 95% confidence level are obtained on the masses of the dark matter particle and its mediator.

Large magneto-optical effects and magnetic anisotropy energy in two-dimensional Cr 2 Ge 2 Te 6

Abstract: Atomically thin ferromagnetic (FM) films were recently prepared by mechanical exfoliation of bulk FM semiconductor ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$. They provide a platform to explore novel two-dimensional (2D) magnetic phenomena, and they offer exciting prospects for new technologies. By performing systematic ab initio density functional calculations, here we study two relativity-induced properties of these 2D materials (monolayer, bilayer, and trilayer as well as bulk), namely magnetic anisotropy energy (MAE) and magneto-optical (MO) effects. Competing contributions of both magnetocrystalline anisotropy energy (C-MAE) and magnetic dipolar anisotropy energy (D-MAE) to the MAE are computed. The calculated MAEs of these materials are large, being on the order of $\ensuremath{\sim}0.1$ meV/Cr. Interestingly, we find that out-of-plane magnetic anisotropy is preferred in all the systems except the monolayer, where in-plane magnetization is favored because here the D-MAE is larger than the C-MAE. Crucially, this explains why long-range FM order was observed in all the few-layer ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ except the monolayer because the out-of-plane magnetic anisotropy would open a spin-wave gap and thus suppress magnetic fluctuations so that long-range FM order could be stabilized at finite temperature. In the visible frequency range, large Kerr rotations up to $\ensuremath{\sim}2.{2}^{\ensuremath{\circ}}$ in these materials are predicted, and they are comparable to that observed in famous MO materials such as PtMnSb and ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$. Moreover, they are $\ensuremath{\sim}100$ times larger than that of $3d$ transition metal monolayers deposited on Au surfaces. Faraday rotation angles in these 2D materials are also large, being up to $\ensuremath{\sim}{120}^{\ensuremath{\circ}}/\ensuremath{\mu}\mathrm{m}$, and they are thus comparable to the best-known MO semiconductor ${\mathrm{Bi}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$. These findings thus suggest that with large MAE and MO effects, atomically thin ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ films would have potential applications in novel magnetic, MO, and spintronic nanodevices.

Equation of state for dense nucleonic matter from metamodeling. II. Predictions for neutron star properties

Abstract: Employing recently proposed metamodeling for the nucleonic matter equation of state, we analyze neutron star global properties such as masses, radii, momentum of inertia, and others. The impact of the uncertainty on empirical parameters on these global properties is analyzed in a Bayesian statistical approach. Physical constraints, such as causality and stability, are imposed on the equation of state and different hypotheses for the direct Urca (dUrca) process are investigated. In addition, only metamodels with maximum masses above $2{M}_{\ensuremath{\bigodot}}$ are selected. Our main results are the following: the equation of state exhibits a universal behavior against the dUrca hypothesis under the condition of charge neutrality and $\ensuremath{\beta}$ equilibrium; neutron stars, if composed exclusively of nucleons and leptons, have a radius of $12.7\ifmmode\pm\else\textpm\fi{}0.4$ km for masses ranging from 1 up to $2{M}_{\ensuremath{\bigodot}}$; a small radius lower than 11 km is very marginally compatible with our present knowledge of the nuclear empirical parameters; and finally, the most important empirical parameters which are still affected by large uncertainties and play an important role in determining the radius of neutrons stars are the slope and curvature of the symmetry energy (${L}_{\mathrm{sym}}$ and ${K}_{\mathrm{sym}}$) and, to a lower extent, the skewness parameters (${Q}_{\mathrm{sat}/\mathrm{sym}}$).

Constraining Primordial Black Holes with the EDGES 21-cm Absorption Signal : arXiv

Abstract: The EDGES experiment has recently measured an anomalous global 21-cm spectrum due to hydrogen absorptions at redshifts of about $z\ensuremath{\sim}17$. Model independently, the unusually low temperature of baryons probed by this observable sets strong constraints on any physical process that transfers energy into the baryonic environment at such redshifts. Here, we make use of the 21-cm spectrum to derive bounds on the energy injection due to a possible population of $\mathcal{O}(1--100){M}_{\ensuremath{\bigodot}}$ primordial black holes, which induce a wide spectrum of radiation during the accretion of the surrounding gas. After calculating the total radiative intensity of a primordial black hole population, we estimate the amount of heat and ionizations produced in the baryonic gas and compute the resulting thermal history of the Universe with a modified version of RECFAST code. Finally, by imposing that the temperature of the gas at $z\ensuremath{\sim}17$ does not exceed the indications of EDGES, we constrain the possible abundance of primordial black holes. Depending on uncertainties related to the accretion model, we find that $\mathcal{O}(10){M}_{\ensuremath{\bigodot}}$ primordial black holes can only contribute to a fraction ${f}_{\mathrm{PBH}}l(1--{10}^{\ensuremath{-}3})$ of the total dark matter abundance.

Energy-Aware Spiral Coverage Path Planning for UAV Photogrammetric Applications

Abstract: Most unmanned aerial vehicles nowadays engage in coverage missions using simple patterns, such as back-and-forth and spiral. However, there is no general agreement about which one is more appropriate. This letter proposes an E-Spiral algorithm for accurate photogrammetry that considers the camera sensor and the flight altitude to apply the overlapping necessary to guarantee the mission success. The algorithm uses an energy model to set different optimal speeds for straight segments of the path, reducing the energy consumption. We also propose an improvement for the energy model to predict the overall energy of the paths. We compare E-Spiral and E-BF algorithms in simulations over more than 3500 polygonal areas with different characteristics, such as vertices, irregularity, and size. Results showed that E-Spiral outperforms E-BF in all the cases, providing an effective energy saving even in the worst scenario with a percentage improvement of $10.37\%$ up to the best case with $\text{16.1}\%$ of improvement. Real flights performed with a quadrotor state the effectiveness of the E-Spiral over E-BF in two areas, presenting an improvement of $\text{9}\%$ in the time and $\text{7.7}\%$ in the energy. The improved energy model increases the time and the energy estimation precision of $\text{13.24}\%$ and $\text{13.41}\%$ , respectively.

Data-driven prediction of the high-dimensional thermal history in directed energy deposition processes via recurrent neural networks

Abstract: Directed Energy Deposition (DED) is a growing additive manufacturing technology due to its superior properties such as build flexibility at multiple scales and limited waste. However, both experimental and physics-based models have limitations in providing accurate and computationally efficient predictions of process outcomes, which is essential for real-time process control and optimization. In this work, a recurrent neural network (RNN) structure with a Gated Recurrent Unit (GRU) formulation is proposed for predicting the high-dimensional thermal history in DED processes with variations in geometry, build dimensions, toolpath strategy, laser power and scan speed. Our results indicate that the model can accurately predict the thermal history of any given point of the DED build on a test-set database with limited training. The model’s general applicability and ability to accurately predict thermal histories has been demonstrated through two overarching tests conducted for long time spans and non-trained geometries.

High-Density NAND-Like Spin Transfer Torque Memory With Spin Orbit Torque Erase Operation

Abstract: We present a NAND-like spintronics memory (NAND-SPIN) device for high-density non-volatile memory applications. Fast erasing and programming of magnetic tunnel junction (MTJ) are implemented with two unidirectional currents generating spin orbit torque (SOT) and spin transfer torque (STT), respectively. The asymmetric switching drawback of STT mechanism can be definitively overcome as only anti-parallel to parallel operation happens for NAND-SPIN programming, which allows lower switching current, smaller access transistor, and reduced maximum write voltage across the MTJ. By sharing the SOT-induced erase operation in a nanowire, the area overhead due to the three-terminal structure can be also eliminated. Simulation results show that NAND-SPIN can achieve $\text {3}\sim \text {5}\times $ reduction in write energy compared to STT-MRAM, and $\text {2}\sim \text {4}\times $ less bit-cell area than SOT-MRAM at 28 nm node.

On-the-Fly Machine Learning of Atomic Potential in Density Functional Theory Structure Optimization.

Abstract: Machine learning (ML) is used to derive local stability information for density functional theory calculations of systems in relation to the recently discovered ${\mathrm{SnO}}_{2}(110)\text{\ensuremath{-}}(4\ifmmode\times\else\texttimes\fi{}1)$ reconstruction. The ML model is trained on (structure, total energy) relations collected during global minimum energy search runs with an evolutionary algorithm (EA). While being built, the ML model is used to guide the EA, thereby speeding up the overall rate by which the EA succeeds. Inspection of the local atomic potentials emerging from the model further shows chemically intuitive patterns.

Permutation Index DCSK Modulation Technique for Secure Multiuser High-Data-Rate Communication Systems

Abstract: A new noncoherent scheme called Permutation Index Differential Chaos Shift Keying (PI-DCSK) modulation is proposed in this paper. This original design aims to enhance data security, energy and spectral efficiencies, compared to its rivals. In the proposed PI-DCSK scheme, each data frame is divided into two time slots in which the reference chaotic signal is sent in the first time slot and a permuted replica of the reference signal multiplied by the modulating bit is sent in the second time slot. In particular, the bit stream is divided at the transmitter into blocks of $n+1$ bits, where $n$ mapped bits are used to select one of the predefined reference sequence permutations, while a single modulated bit is spread by the permuted reference signal just mentioned. At the receiver side, the reference signal is recovered first, then all permuted versions of it are correlated with the data-bearing signal. The index of the correlator output with maximum magnitude will estimate the mapped bits, while the output content of the corresponding correlator is compared to a zero threshold to recover the modulated bit. Moreover, a new multiple access method based on the proposed scheme is described and analysed. Analytical expressions for the error performance in single-user and multiuser environments are derived for additive white Gaussian noiseand multipath Rayleigh fading channels, respectively. Furthermore, the performance of the proposed PI-DCSK system is analysed and compared with other noncoherent chaotic modulation schemes and is found to be promising.

Three-dimensional droplets of swirling superfluids

Abstract: A method for the creation of three-dimensional (3D) solitary topological modes, corresponding to vortical droplets of a two-component dilute superfluid, is presented. We use the recently introduced system of nonlinearly coupled Gross-Pitaevskii equations, which include contact attraction between the components, and quartic repulsion stemming from the Lee-Huang-Yang correction to the mean-field energy. Self-trapped vortex tori, carrying the topological charges ${m}_{1}={m}_{2}=1$ or ${m}_{1}={m}_{2}=2$ in their components, are constructed by means of numerical and approximate analytical methods. The analysis reveals stability regions for the vortex droplets (in broad and relatively narrow parameter regions for ${m}_{1,2}=1$ and ${m}_{1,2}=2$, respectively). The results provide a scenario for the creation of stable 3D self-trapped states with the double vorticity (${m}_{1,2}=2$). The stable modes are shaped as flat-top ones, with the space between the inner hole, induced by the vorticity, and the outer boundary filled by a nearly constant density. On the other hand, all modes with hidden vorticity, i.e., topological charges of the two components ${m}_{1}=\ensuremath{-}{m}_{2}=1$, are unstable. The stability of the droplets with ${m}_{1,2}=1$ against splitting (which is the main scenario of possible instability) is explained by estimating analytically the energy of the split and unsplit states. The predicted results may be implemented, exploiting dilute quantum droplets in mixtures of Bose-Einstein condensates.

ECRAM as Scalable Synaptic Cell for High-Speed, Low-Power Neuromorphic Computing

Abstract: We demonstrate a nonvolatile Electro-Chemical Random-Access Memory (ECRAM) based on lithium (Li) ion intercalation in tungsten oxide (WO 3 ) for high-speed, low-power neuromorphic computing. Symmetric and linear update on the channel conductance is achieved using gate current pulses, where up to 1000 discrete states with large dynamic range and good retention are demonstrated. MNIST simulation based on the experimental data shows an accuracy of 96%. For the first time, high-speed programming with pulse width down to 5 ns and device operation at scales down to $300\times 300\ \text{nm}^{2}$ are shown, confirming the technological relevance of ECRAM for neuromorphic array implementation. It is also verified that the conductance change scales linearly with pulse width, amplitude and charge, projecting an ultralow switching energy ∼1 fJ for $100\times 100\ \text{nm}^{2}$ devices.

Robust non-Abelian spin liquid and a possible intermediate phase in the antiferromagnetic Kitaev model with magnetic field

Abstract: We investigate the non-Abelian topological chiral spin-liquid phase in the two-dimensional Kitaev honeycomb model subject to a magnetic field. By combining density matrix renormalization group and exact diagonalization we study the energy spectra, entanglement, topological degeneracy, and expectation values of Wilson loop operators, allowing for a robust characterization. While the ferromagnetic Kitaev spin liquid is already destroyed by a weak magnetic field with Zeeman energy ${H}_{*}^{\text{FM}}\ensuremath{\approx}0.02$, the antiferromagnetic (AFM) spin liquid remains robust up to a magnetic field that is an order of magnitude larger, ${H}_{*}^{\text{AFM}}\ensuremath{\approx}0.2$. Interestingly, for larger fields ${H}_{*}^{\text{AFM}}lHl{H}_{**}^{\text{AFM}}$, an intermediate gapless phase is observed, before a second transition to the high-field partially polarized paramagnet. We attribute this rich phase diagram, and the remarkable stability of the chiral topological phase in the AFM Kitaev model, to the interplay of strong spin-orbit coupling and frustration enhanced by the magnetic field. Our findings suggest relevance to recent experiments on ${\mathrm{RuCl}}_{3}$ under magnetic fields.